In DC-DC converters (also called DC choppers), for example in the form of push-pull forward converters, the stray inductances of the usually used transformers in conjunction with the commutation behavior of the secondary-side rectifier diodes produce switching overvoltages across the power semiconductors, which switching overvoltages would lead to destruction of the power semiconductors if not limited or would require extreme oversizing of the dielectric strength.
Conventionally, RC elements are connected in parallel with the rectifier diodes of the DC-DC converters in order to damp the switching overvoltages. One disadvantage of this is the resulting heat loss in the damping resistors. Depending on the current load, switching energy, temperature etc., this can result in considerable problems in respect of heat dissipation which can lead to the achievable output current being limited.
The invention is based on the problem of providing a DC-DC converter which ensures effective protection switching overvoltages and which at the same time produces as little electrical loss as possible.
The invention solves this problem by virtue of a DC-DC converter comprising: an output terminal, wherein the output terminal comprises a first output terminal pin and a second output terminal pin; a number of rectifier elements; a voltage limiting unit comprising an electrical energy store, wherein the voltage limiting unit is designed to limit voltages across the rectifier elements; and a clocked energy regulator unit which is designed to regulate at a setpoint value energy which is stored in the electrical energy store.
The invention relates to a DC-DC converter, in particular in the form of a push-pull forward converter. The DC-DC converter can be of unidirectional or bidirectional design.
The DC-DC converter has an output terminal, wherein the output terminal has a first output terminal pin (positive pole) and a second output terminal pin (negative pole). A higher potential can be produced at the first output terminal pin than at the second output terminal pin. Here, the term “output” is not intended to be understood in a restrictive manner to the effect that it necessarily has to be a unidirectional DC-DC converter comprising a dedicated input and output. In the case of a bidirectional DC-DC converter, the output terminal is one of the two (non-directional) outer terminals.
The DC-DC converter further has a number of (for example between 2 and 4) rectifier elements.
The DC-DC converter further has a, in particular passive, voltage limiting unit (overvoltage protection unit). The voltage limiting unit is designed to limit or to reduce (over) voltages across the rectifier elements. The voltage limiting unit has an electrical energy store which is designed to at least partially buffer-store energy which originates from voltage peaks due to switching processes.
The DC-DC converter further has a clocked energy regulator unit which is coupled to the voltage limiting unit and is designed to limit and/or regulate at a setpoint value energy which is stored in the electrical energy store or a voltage which is present at the energy store by the energy regulator unit transmitting, for example, energy which is stored in the energy store in the direction of the output terminal when the energy which is stored in the energy store exceeds an energy setpoint value or a voltage which is present at the energy store exceeds a voltage threshold value. The energy regulator unit may comprise a clocked switching means, wherein a clock of the switching means can differ from an operating clock of the DC-DC converter.
The energy regulator unit allows switching energy to be provided in a regenerative manner, for example, at the output terminal, without the switching energy being converted into heat in a dissipative manner in a resistor. Effective overvoltage limiting is ensured at the same time.
The clocked energy regulator unit may comprise a (clocked) DC chopper (can generally also be called a clocked chopper), for example in the form of an inverse converter, which is designed to transmit energy which is stored in the electrical energy store in the direction of the output terminal. The DC chopper can function as an actuator in the context of energy or voltage regulation, for example by transmitting energy in the direction of the output terminal only when the energy which is stored in the electrical energy store exceeds a setpoint value. The DC chopper can be, for example, an inverting or a non-inverting buck converter or boost converter.
The DC-DC converter may comprise a, for example DC-isolating, transformer. The transformer has, in addition to one, two or more primary windings, at least one secondary winding, wherein the rectifier elements are designed to rectify one or more voltages across the at least one secondary winding.
The transformer may comprise precisely one first secondary winding and precisely one second secondary winding, wherein the rectifier elements are designed to rectify voltages across the first and the second secondary winding.
The rectifier elements can be diodes. As an alternative, the rectifier elements can also be transistors, for example MOSFETs, as a result of which synchronous rectification is possible.
The DC-DC converter may comprise an inductive component, for example in the form of a coil or inductor. A first terminal of the first secondary winding and a first terminal of the second secondary winding can be indirectly (with further interposed components) or directly (without further interposed components) electrically connected to the second output terminal pin. The first rectifier element and the inductive component can be looped in between a second terminal of the first secondary winding and the first output terminal pin. The second rectifier element can be looped in between a second terminal of the second secondary winding and a connecting node of the first rectifier element and of the inductive component.
The voltage limiting unit may comprise a first diode and a second diode. The electrical energy store can be a capacitor or comprise a capacitor. The anode of the first diode and the anode of the second diode can be electrically connected to a first terminal of the capacitor. The cathode of the first diode can be electrically connected to the second terminal of the first secondary winding. The cathode of the second diode can be electrically connected to the second terminal of the second secondary winding. A second terminal of the capacitor can be electrically connected to a connecting node of the first rectifier element, of the second rectifier element and of the inductive component.
The energy regulator unit may comprise a decoupling diode and a charge transfer capacitor. The cathode of the decoupling diode can be electrically connected to the anode of the first diode and to the anode of the second diode. A first terminal of the charge transfer capacitor can be electrically connected to the anode of the decoupling diode. A second terminal of the charge transfer capacitor can be electrically connected to the second output terminal pin. A first input terminal pin of the DC chopper can be electrically connected to the cathode of the decoupling diode. A second input terminal pin of the DC chopper can be electrically connected to the first terminal of the first secondary winding, to the first terminal of the second secondary winding and to the second output terminal pin.
In an alternative embodiment, the DC-DC converter may comprise an inductive component, for example in the form of an inductor or coil, wherein the inductive component is looped in between a connecting node of a first terminal of the first secondary winding and of a first terminal of the second secondary winding and the first output terminal pin. The first rectifier element can be looped in between a second terminal of the second secondary winding and the second output terminal pin. The second rectifier element can be looped in between a second terminal of the first secondary winding and the second output terminal pin.
In this case, the voltage limiting unit may comprise a first diode and a second diode. The electrical energy store can be a capacitor. The cathode of the first diode and the cathode of the second diode can be electrically connected to a first terminal of the capacitor. The anode of the first diode can be electrically connected to the second terminal of the first secondary winding. The anode of the second diode can be electrically connected to the second terminal of the second secondary winding. A second terminal of the capacitor can be connected to the second output terminal pin.
A first input terminal pin of the DC chopper can be electrically connected to the cathode of the first diode, to the cathode of the second diode and to the first terminal of the capacitor. A second input terminal pin of the DC chopper can be electrically connected to the second output terminal pin and to the second terminal of the capacitor.
The transformer may comprise at least one primary winding. The DC-DC converter may comprise at least one clocked half-bridge circuit which is designed to apply a voltage which varies over time or a current which varies over time to at least one primary winding. In this case, the DC-DC converter (or a control unit of the DC-DC converter) is designed to set a switching frequency of the at least one half-bridge circuit independently of a switching frequency of the clocked energy regulator unit or of the DC chopper and/or to set switching phases of the at least one half-bridge circuit independently of switching phases of the clocked energy regulator unit or of the DC-DC converter. By way of example, the half-bridge circuit can carry out a pulse width modulation and the energy regulator unit can likewise carry out a pulse width modulation, wherein both the respective period durations and also the respective duty cycles of the pulse width modulation can be set independently of one another.
The transformer may comprise a first primary winding and a second primary winding. The DC-DC converter may comprise a first clocked half-bridge circuit and a second clocked half-bridge circuit, wherein the first clocked half-bridge circuit is designed to apply a voltage which varies over time or a current which varies over time to the first primary winding, and the second clocked half-bridge circuit is designed to apply a voltage which varies over time or a current which varies over time to the second primary winding. In this case, the DC-DC converter is designed to set a switching frequency of the first clocked half-bridge circuit and of the second clocked half-bridge circuit independently of a switching frequency of the clocked energy regulator unit or of the DC chopper and/or to set switching phases of the first clocked half-bridge circuit and of the second clocked half-bridge circuit independently of switching phases of the clocked energy regulator unit or of the DC chopper.